The importance of hydrogen gas in the chemical industry has long been known. Hydrogen is currently obtained as a by-product in certain processes [3, 12, 14, 26]: catalytic reforming in oil refineries or electrolysis of molten sodium chloride or sodium chloride in aqueous solution. Refineries completely consume the hydrogen produced by their reforming systems to improve the octane number of gasoline, requiring enormous additional amounts of H2 for their processes that eliminate contents of precursor atoms of pollutants (mainly S) in gases, gasolines and diesel oils, which forces them to have large specific hydrogen manufacturing plants. This consumption is furthermore increasing as lower sulfur contents in petroleum derivatives are being required according to the environmental legislation.
However, together with traditional markets for hydrogen: steel and metallurgical industries, glass manufacturing etc., there are emerging markets, among which that related to the transport sector, either in vehicles with internal combustion engines, burning hydrogen as a fuel, or in vehicles using it in fuel cells feeding electric engines, must be highlighted [6,18,20]. A fundamental characteristic of these new markets is the fact that they generate a number of consumption points that are completely dispersed over the geography of any developed country. The alternative of distributing hydrogen according to the traditional method with which gasoline and gas oil are distributed (trailers) causes serious drawbacks associated to safety and cost problems. An enormously interesting alternative would be the development of technologies which allow manufacturing hydrogen in situ, provided that the consumption justifies it.
The most interesting raw material for manufacturing hydrogen for these purposes is natural gas and its main component, methane (CH4) (approximately 90% by volume of natural gas), given the wide distribution network existing for this fuel and the existence of technologies for converting it into hydrogen.
The most important processes that are currently used for producing hydrogen from methane are four in number [13]: steam reforming, partial oxidation, combination of oxidation and reforming (system referred to as autothermal reforming) and catalytic decomposition.
Steam reforming consists of the catalytic transformation of methane and steam in hydrogen and carbon oxides. Several reactions may occur [11]:
1) Main reaction (reforming):CH4+H2O═CO+3H2 ΔH°(298 K)=206.14 kJ/mol
2) Shift reaction:CO+H2O═CO2+H2 ΔH°(298 K)=−41.17 kJ/mol
3) Carbon deposition reactions (unwanted):2CO═C(s)+CO2 
Other reactions may occur in the process but they would depend on the three written reactions.
The reforming reaction is favored at high temperatures (760-925° C.) and low pressures. The catalysts that are most used are formed by nickel supported on alumina. The reformer is fed with excess water to prevent carbon formation. The most usual molar water/methane feed ratios are comprised between 2 and 5.
The steam reforming is the process that is most used on an industrial scale and is the most studied and known one. It is the process whereby a larger hydrogen production is obtained. In this case, heat transmission is critical because the reaction is strongly endothermic. Enormous and very complex reforming ovens are therefore needed. This complexity and the associated costs make this process be only economically viable for large productions. It must be noted, however, that ongoing developments attempt to generate more compact reforming technologies the economical viability of which can be reached for smaller productions in the mid-term future (1).
CO is produced in this process, therefore in processes in which the produced gas is used, which do not tolerate the presence of this compound, it will be necessary to place after the reformer systems reducing the CO concentration to the necessary concentration for the good operation of the process in question.
The partial oxidation process consists of the catalytic oxidation reaction of methane [32].CH4+0.5O2═CO+2H2 ΔH°(298K)=−36 kJ/mol
The reaction takes place at high temperatures (T>800° C.) in excess methane. The molar O2/CH4 feed ratio is usually comprised between 0.5 and 1. The oxygen source can be air, oxygen-enriched air or pure oxygen. Multiple catalysts have been developed for this process. The most used metals are platinum and nickel supported on a ceramic material. One of the problems of this process is carbon deposition, involving a fast deactivation of the catalyst.
The hydrogen production is less than that obtained in a steam reforming process and is therefore less efficient. The main advantage of this process is its exothermicity and this leads to the need for little physical space and a fast ignition. It is furthermore insensitive to load variation and the general cost is relatively low (2).
As in the reforming process, to reduce the CO content it is necessary to place after the reactor systems eliminating it to a suitable concentration so as to be able to feed the subsequent application, if the latter requires so.
Another hydrogen production process is the so-called “Catalytic Natural Gas Decomposition”. The process is essentially an endothermic reaction in which methane decomposition occurs to yield solid carbon and hydrogen [13]. The hydrogen produced increases when the temperature increases and the pressure decreases.CH4═C(s)+2H2 ΔH°(298 K)=75 kJ/mol
Catalytic natural gas decomposition produces highly pure hydrogen which does not require any subsequent purification step. The need to work with two reactors in parallel to use the energy produced in the regeneration of the catalyst involves an increase in the reformer size. But its main drawback lies in the fact that all the carbon present in the methane ends up as soot in the catalytic bed and the regeneration of the latter requires its almost-complete combustion with air, whereby the chance to generate additional amounts of H2 by the subsequent reforming of CO is lost. Furthermore, these cycles of reactivation by combustion, in which high temperatures are reached, cause accelerated deactivations of the catalysts involved.
Autothermal reforming (ATR) is a combination of catalytic and non-catalytic partial oxidation and steam reforming, such that the heat produced in the oxidation reactions is used, after the subsequent steam feed, for steam reforming, being overall an adiabatic reactor. This allows the reactor to be much more compact than in the other processes.
The hydrogen production is comprised between that obtained in steam reforming and that obtained in catalytic partial oxidation. In addition, if steam were added in the feed carbon deposition would be prevented and the high temperature peak occurring in the initial area of the catalytic bed, which is typical of methane combustion, would be reduced [4,11].
This hydrogen production system therefore has the following advantages:                Maximum methane conversion.        High yield in the hydrogen production.        Minimum energy consumption.        Minimum generation of secondary pollutants (NOX)        Compact size.        Low fixed and variable costs        Quick start and response to load variations.        Quick operation and maintenance.        
From that set forth, it is deduced that partial oxidation and autothermal reforming processes are the most suitable processes, the latter being chosen to achieve this project.
This type of reactors currently consists of an area in which oxidation occurs and another area in which steam reforming occurs [32], using different catalysts in each area of the reactor (in some processes the partial oxidation step is carried out by means of a non-catalytic process). In these reactors, the combustion with oxygen shortage occurs first, to subsequently inject steam in an amount and at a pressure and temperature that are suitable for, in adiabatic conditions, the reforming reactions of the methane that has not reacted, and mainly of the carbon monoxide produced, to occur.
The type of reactor usually used in industrial processes [12, 26] is the fixed bed reactor due to the compactness, due to the simplicity in its design and low cost.
Most industrial processes (large scale plants) operate at pressures above 25 atm, which makes the installations more compact for the feed flows which are used.
In large scale industrial plants, the operation is carried out at very high temperatures, above 1200° C., so as to obtain high conversions since very high pressures are used in the operation. These so severe operating conditions require special materials which are very expensive.
There are two large groups of catalysts used to obtain synthesis gas: Ni-based catalysts and noble metal-based catalysts.
Ni-based catalysts supported on Mg—Al2O3 are generally used in industrial steam reforming processes and are the most extensively studied. However, they are also used in partial oxidation and autothermal reforming processes [10], although they are not specific for these processes. Said catalysts have a very high turnover number (number of molecules reacting per active site per second), high heat stability and low cost, in addition to a good behavior in wide temperature intervals (450-900° C.) and, above 700° C., they have CO selectivities close to 95% and conversions close to 100%. However, their main drawback is that they have a fast deactivation due to carbon deposition on the surface of the catalyst particles.
Several studies of Ni catalysts supported on La2O3, MgO or ZrO2 having advantages in partial oxidation processes have been found in the literature [10, 25, 28, 31].
Noble metal-based catalysts seem to be more active in partial oxidation and autothermal reforming reactions than nickel-based catalysts, but are about 150 times more expensive (3). Ru is the least expensive among the noble metals and is more stable than nickel. At low concentrations on an Al2O3 support, it is more active and selective than Ni. If SiO2 is used as the support, Ru can oxidize methane at temperatures of 400° C. [12].
The choice of the support and the conditions for preparing the catalysts are essential in the behavior in the conversion, selectivity and useful life of the catalyst and, in this sense, efforts are being made in the search for new catalysts.
Avci et al. [4] studied the autothermal reforming reactions in a reactor containing a mixture of Ni—Al2O3 and Pt—Al2O3 catalysts, observing that the hydrogen production is greater than when each catalyst is located in two different beds of the reactor and when the O2/CH4 and H2O/CH4 ratios are increased.
The latest studies in this field intend that this process does not occur in two steps (initial combustion with oxygen shortage and subsequent reforming with steam injected in this second step to generate additional hydrogen, using the energy contained in the high temperature gases generated in the incomplete initial combustion) but rather in a single catalytic step to which natural gas, air (or oxygen) and steam would be fed, which would generate a much more compact reaction system (23).
To cover these needs and overcome the drawbacks of the prior art, the authors have carried out a new system in which natural gas, oxygen and steam are fed simultaneously and react on the same catalyst, such that the partial oxidation and steam reforming reactions occurs almost simultaneously, giving rise to a wet catalytic partial oxidation, wet CPO, which allows developing a hydrogen obtaining system for production levels that are much lower than the usual ones in current conventional reforming plants, “in situ” and economically competitive with its distribution from centralized plants.